I put (with help from JRH) a 203mm Hayes Stroker on the front of my mountain e-bike, and they have worked out quite well.
On the rear I went with Shimano XTR, with parallelogram pad motion, a very high end rim brake, because there are no disc brake mounts on this old Novara frame (I really should get regen going, that would probably reduce or eliminate the need for the rear brakes):
On the heavier and faster Greyborg I used dual 160mm disc 4 pot Gatorbrakes in the front:
And then recently updated the Borg with the new 203mm Tektro Auriga e-brakes that have built in switch and a parking switch that locks them on:
On the Greyborg's rear brake there is not much room alongside the Cromotor so I'm using e-braking with the modified Sabvoton controller from zombiess. This has plenty of capability for a rear brake, I have adjusted it to almost skid the rear tire on dry pavement, and during testing had plenty of settings that produced skidding so I know it is capable. I can't use much more rear braking than that in the rear wheel.
Regen as a rear brake is not ideal from a reliability standpoint, it requires the controller, motor and battery to be working, and the battery must not be too full to accept charging (unless your regen has a plug braking (resistive load) option). But it doesn't wear your pads/shoes, and it produces some charging to the battery (generally not a lot). Some batteries won't accept charging very fast which limits the amount of regen braking that can be used, and many controllers have poor control over the braking amount. But for descending long grades they work well and keep your brakes cool for that emergency stop you might need.
When it comes to disc vs rim brakes, a couple of things I've experienced - not all rims are set up for rim brakes (such as moped or motorcycle rims), and not all frames have the right mounts in the right place, especially when changing wheel sizes. Smoking hot disc brakes don't cause problems for the tire or tube and they don't cause rim wear. When discs wear they are much easier to replace than rims. The higher temperature helps them dry quickly in wet weather, and their height above the surface reduces their getting wet from surface grass and mud. Rim brakes aren't used on mopeds or motorcycles, they are really optimal for low weight low inertia machines but not so much for higher power/speed/momentum applications. It seems to me that rim brakes require more fiddling than discs to keep them from squealing and properly adjusted. Just a touch of moisture shuts them off and they don't dry out easily or stay dry long.
Based on what I've seen I'd advocate a front disc, or dual disc while on the rear anything should be adequate - rim, disc, or regen. I haven't worked with drums since my moped and they were a weak point there, but modern drums may be a different story.
plug brake is what i was looking for
